The need for biobased reagents, chemicals and products replacing oil-based, traditional raw materials is constantly growing. Applications for this bioreplacement are entering new fields.
Terephtalic acid is the main monomer of the dominant polyester polymers, finding wide use in textiles, technical applications, packaging especially bottles and films. One of these polymers, polyethylene terephtalate (PET) is a thermoplastic polymer resin of the polyester family and is used in synthetic fibres. It has several benefits like high transparency, low weight, very good mechanical characteristics, good barrier properties, good form stability, high recyclability, health authorities' approval (e.g. FDA, EU) and economic production.
For bioreplacement in polyethylene terephtalate (PET) and polybutylene terephtalate (PBT) it is essential to find efficient production routes for the terephtalic acid. Para-cymene (p-cymene) is a common precursor for oxidative production of terephtalic acid of plant-based limonene, terpinenes, and pinenes, which are recoverable in citrus fruit peals, tee three oil, turpentine respectively, and through isoprenoid pathway of carbohydrates. When applying commercial oxidation process for the cymene, yield of 90% of terephtalic acid is achieved.
It is desirable to increase the value of crude sulfur turpentine (CST) by converting it to a more valuable chemical, such as p-cymene. p-Cymene is an aromatic hydrocarbon that can be utilized as raw material in the synthesis of polymers, but there are also many other applications for p-cymene e.g. in the production of fine chemicals (Monteiro, J. L. F., Veloso, C. O., Catalytic conversion of terpenes into fine chemicals, Top. Catal. 27 1-4 (2004) 169-180). Industrially, p-cymene is produced by alkylation of toluene with propene.
Worldwide production of pinenes was 0.33 Mton/year based on FAO statistics on 1995. Of this 70% was sulfate turpentine CST from wood in chemical pulping processes, consisting 90% alpha- and beta-pinenes. However, the pulping process originated aromates contain sulfur, which causes problems in further refinement of pinenes, especially poisoning the catalyst and leaving an unacceptable odor to PET eventually produced from terphtalate.
Some processes for the conversion of pinenes into cymenes are known. Determination of liquid phase reaction conditions and selection of catalyst for preparation of p-cymene from α-pinene has been reviewed by Wang (Huaxue Shijie (2001), 42(3), 131-133 CODEN: HUAKAB; ISSN: 0367-6358). The preparation of p-cymene from α-pinene was studied by ring-opening-isomerization and hydrogen transfer disproportionation with a catalyst like Raney nickel, copper formate, and p-toluenesulfonic acid.
Pinenes can be dehydrogenated and aromatized in presence of Pd-catalyst close to atmospheric pressure and 200-400° C. temperature, based on Hörderlich, Applied Catalysis, A: General (2001), 215(1-2),111-124 CODEN: ACAGE4; ISSN: 0926-860X. The dehydrogenation of α-pinene to p-cymene is conducted over carriers impregnated with Pd. An optimal acid strength is required to cleave selectively the C—C bond in the cyclobutane ring of α-pinene. Too strong acid sites such as in zeolites favor side reactions like oligomerization and cracking Too weak acid sites fail to cleave the aforementioned C—C bond and rapid hydrogenation of the α-pinene is a consequence. Hydrogenolysis is also a major side reaction leading to tetramethylcyclohexanes. A reaction mechanism is proposed in which first isomerization is involved followed by hydrogenation/dehydrogenation to stabilize the components. The catalyst has a dual-functionality with the acid sites in charge of isomerization and the metallic sites responsible of hydrogenation/dehydrogenation. The use of crude sulfate turpentine (CST) as raw material shows that β-pinene has a similar reactivity as α-pinene and high yields of p-cymene can be obtained from this cheap starting material. The sulfur remains however a major drawback. The process yields 65% from pinenes and 59% of the turpentines. However, when applying CST, sulfur must be removed, because it poisons the catalyst rapidly.
Bazhenov et al. in Russian Journal of Applied Chemistry (Translation of Zhurnal Prikladnoi Khimii) (2003), 76(2), 234-237 CODEN: RJACEO; ISSN: 1070-4272, reported hydrogenation and isomerization of α-pinene on zeolite Y and heterogeneous nickel catalysts. Nickel catalyst supported on alumina reached 80% conversion in 2 hours at 400-450° C. and 0.5 MPa hydrogen pressure. However, nickel is especially sensitive for sulfur.
Kutuzov et al. disclose in RU 2200144, a process for skeletal isomerization and dehydrogenation of α-pinene in presence of zeolite-containing cracking catalyst (Z-10) preliminarily activated for 1-2 hours at 300-550° C. in nitrogen flow. Process is carried out for 2-8 hours at 150-170° C. and 5 atmospheric nitrogen pressure. The reaction is typically robust for sulfur and yields 80% conversion to p-cymene.
However, even when not harmful for the process, the remaining sulfur may be undesirable in the end products, i.e. in plastics intended for food packages. As such, it requires separate processes for sulfur removal. Removal of sulfur-containing compounds from sulfate wood turpentine has been studied widely.
Chudinov et al. disclose in SU 332115 removal of sulfur impurities from turpentine oil by treatment with sodium hypochlorite solution in the presence of a mineral acid.
Another document, U.S. Pat. No. 3,778,485 discloses purification of crude sulfate turpentine by agitating with sodium hypochlorite solution containing 90 g/l available Cl followed by washing. The composition of the bleached turpentine was α-pinene 76.4, camphene 1.3, β-pinene 13.8, myrcene 2.2, dipentene 3.6, pine oil 2, heavies 0.6, S (weight/volume) 0.014, and chloride (weight/volume) 0.092.
In U.S. Pat. No. 3,778,486, the turpentine hydrocarbon fraction was desulfurized by a multistage activated carbon (C) sorption process. Thus, the turpentine fraction containing 500 ppm of sulfur (S) was first stripped of light ends boiling below α-pinene, contacted with C, and the S-laden C regenerated in a plurality of steps. The first step was done at 150° C. and continued until the S content in the stripped phase was not substantially >50 ppm S. The second step was done at 250-300° C. and was continued for a time sufficient to remove all S in C.
Further, according to FR 2 243 246 the turpentine hydrocarbon fraction was purified by adsorption with activated C in several stages, each permitting desulfurization.
Otto and Herbst, in Zellstoff and Papier (Leipzig) (1980), 29(2), 59-61 CODEN: ZLPAAL; ISSN: 0044-3867, stated that in the desulfurization of crude turpentine by air-stripping, the amount of Me2S as S compound present in highest concentration in turpentine decreased with increasing stripping time, temperature, and amount of air used. It was calculated that treatment of turpentine containing 710 mg/l Me2S with air of 30 l/h for 83 min produces turpentine oil containing 240 mg/l Me2S.
Matyunina et al. proposed in SU 929676, that variety of sorbents which can be used is expanded by treating sulfate turpentine with a carbonaceous residue resulting from the combustion of ground vegetable fuel having an adsorption activity of 45-50% with respect to iodine and 120-150 g/dm3 bulk density with subsequent regeneration of a sorbent.
Patent EP 243238 discloses a desulfurization catalyst for terpenes obtained in papermaking targeting desulfurizing without significant changes in composition by treatment with H in the vapor phase over Co—Mo oxide catalysts on active charcoal. A terpenic fraction containing α-pinene and 88 ppm S was hydrogenated at 200°/1 atm, space velocity 0.2/h, and H-terpene mol ratio 7:1 over a catalyst containing 7% CoO and 4.4% MoO3 on active charcoal, resulting in 88.6% desulfurization and a 7.3% conversion of terpene; vs. 72 and 54, respectively, when a carene fraction was treated over a CoO—MoO3 catalyst.
Further EP 267833 discloses a catalysts comprising CoO and MoO3 on an inorganic support containing a basic alkali or/and a basic alkaline earth compound. Said catalyst is applicable to the desulfurization of terpenic oils (byproduct from manufacture of paper) by treatment in the vapor phase with H. A catalyst (catalyst A) containing 7 w-% CoO and 4.4 w-% MoO3 was prepared by impregnating silica beads (sp. surface: 250 m-/g; porous volume: 0.6 mL/g) with a solution of Co nitrate and ammonium heptamolybdate, and subsequently drying and calcination at 500° C. for 6 hours. A second catalyst (catalyst B) containing CoO 7, MoO3 4.4, and Na2O 2.5% was prepared similarly except that molybdenum was first introduced in the form of Na2MoO4 and then Co was introduced in the form of its nitrate and that after drying and calcination at 500° C. for 6 hours, the catalyst was impregnated with aqueous NaOH. β-Pinene was treated with catalyst A at 200° and catalyst B at 295° and a H2:terpene ratio of 7. Catalyst A eliminated 95% of the S but with a transformation rate of 85.4% for β-pinene whereas catalyst B showed 95% elimination of S and a β-terpene transformation rate of only 12%. 3-Carene and α-pinene were desulfurized similarly.
Catalytic hydrodesulfurization of terpenes was studied by Casbas et al. (Applied Catalysis (1989), 50(1), 87-97 CODEN: APCADI; ISSN: 0166-9834). Na-doped Co—Mo catalysts were used at 200-280° C. and 1 atm to desulfurize terpene fractions containing α- and β-pinene and Δ3-carene. The best results were obtained with special procedures for Na addition. The surface acidity and isomerizing activity of the catalysts were controlled throughout their preparation by NH3 thermodesorption and certain probe reactions. The presence of thiophenic compounds and, to a lesser extent, the competitive adsorption of terpenes and S-containing molecules could limit the desulfurization.
Further, Casbas et al. (Studies in Surface Science and Catalysis (1991), 59 (Heterog. Catal. Fine Chem. 2), 201-8 CODEN: SSCTDM; ISSN: 0167-2991) have introduced a process and a catalyst for the sulphur removal from turpentine fractions by hydrodesulfurization (HDS) avoiding isomerization and cracking of the terpenes. β-Pinene, one of the most fragile terpenes, was used as a reference throughout the study. Carbons present, alone, a significant HDS activity, but the degradation of β-pinene varies from less than 1% for the most inert support to about 100% for the most active one. On these carbon supports, dipentene is the main product of transformation of β-pinene. Impregnation of cobalt and molybdenum between two layers of sodium ions (sodium molybdate, cobalt nitrate and finally sodium hydroxide) give the best results in HDS of β-pinene: less than 10% degradation and 80% desulfurization.